That gives us a pretty good starting point to understand a lot more about variables, and that's what we'll be examining next lesson. Those new variable types I promised last lesson will finally make an appearance, and we'll examine a few concepts that we'll use to organize our data into more meaningful structures, a sort of precursor to the objects that Cocoa works with. And we'll delve a little bit more into the fun things we can do by looking at those ever-present bits in a few new ways.

When Batman went home at the end of a night spent fighting crime, he put on a suit and tie and became Bruce Wayne. When Clark Kent saw a news story getting too hot, a phone booth hid his change into Superman. When you're programming, all the variables you juggle around are doing similar tricks as they present one face to you and a totally different one to the machine.

A variable leads a simple life, full of activity but quite short (measured in nanoseconds, usually). It all begins when the program finds a variable declaration, and a variable is born into the world of the executing program. There are two possible places where the variable might live, but we will venture into that a little later.

The Stack is just what it sounds like: a tower of things that starts at the bottom and builds upward as it goes. In our case, the things in the stack are called "Stack Frames" or just "frames". We start with one stack frame at the very bottom, and we build up from there.

These secret identities serve a variety of purposes, and they help us to understand how variables work. In this lesson, we'll be writing a little less code than we've done in previous articles, but we'll be taking a detailed look at how variables live and work.